Lignin-assisted double acoustic irradiation for concentrated aqueous dispersions of carbon nanotubes

Abstract

Carbon nanotube (CNTs) dispersion is one of the most challenging tasks for many applications. Lignin-assisted double sonication represents a low-cost and renewable alternative to prepare stable and concentrated suspensions of individualized CNTs.

Cellulose Nanofibril/Carbon Nanomaterial Hybrid Aerogels for Adsorption Removal of Cationic and Anionic Organic Dyes

“…Rice straw was harvested at the South China Agricultural University in 2016. Benzene (99.5%, AR, Damao Chemical Reagent Factory, Tianjin, China), ethanol (99.7%, AR, Guangzhou Chemical Reagent Factory, Guangzhou, China), sodium chlorite (NaClO 2 , 80%, Aladdin), acetic acid glacial (CH 3 COOH, 99.5%, AR, Guangzhou Chemical Reagent Factory), potassium hydroxide (KOH, 85%, AR, Shanghai RichJoint Chemical Reagents, Shanghai, China), hydrochloric acid (HCl, 1 N, certified, Guangzhou Chemical Reagent Factory), sodium hydroxide (NaOH, 96%, Guangzhou Chemical Reagent Factory), sodium hypochlorite (NaClO, 8.0%, AR, Damao Chemical Reagent Factory), 2,2,6,6-tetramethylpyperdine-1-oxyl (TEMPO, 98%, Aladdin), sodium bromide (NaBr, 99.9%, AR, Tianjin Fuchen Chemical Reagent Factory, Tianjin, China), methylene blue (MB, AR, Tianjin Fuchen Chemical Reagent Factory), Congo red (CR, Tianjin Fuchen Chemical Reagent Factory), graphene nanoplates (GnPs, Aldrich, grade C-750, thickness: a few nm, particle size: <2 µm, specific surface area: 750 m 2 g −1 ), and OH-functionalized multi-walled carbon nanotubes (CNTs, Cheap Tubes, external diameter: 50-80 nm, internal diameter: 5-10 nm, length: 10-20 µm, OH content: 5.5%, specific surface area: 60 m 2 g −1 [30]) were used as received. The chemical formula, maximum absorption wavelength and electrical property under neutral pH of MB and CR are shown in Table S1.…”

Lignin-Modified Carbon Nanotube/Graphene Hybrid Coating as Efficient Flame Retardant

“…When lignin was used as the sole coating material ( Figure 2 B), some cellulose nanofibers were still visibly exposed, meaning that lignin did not fully cover the whole paper surface. In all other cases, the absence of visible aggregates yielded relatively flat carbon layers of 25–30 μm in thickness on the paper surface regardless of the type of materials used for coating ( Figure 2 C–F), confirming the good dispersion of carbon nanomaterials during the process [ 28 , 32 ]. This can be attributed to the strong capillary forces of the porous paper, and the resulting large contact area between the coated materials and the cellulose microfibers.…”

“…Previous research reported that the flame-retardant properties of polymer composites with poorly dispersed CNTs did not improve compared to the pristine composites without CNTs [ 39 ]. Owing to its large number of condensed aromatic structures, lignin was adsorbed on GnPs and CNTs via π-π interactions and prevented the nanomaterials from sticking together due to electrostatic repulsion and steric hindrance during the aqueous-phase coating process, as demonstrated elsewhere [ 28 , 32 ]. Moreover, multiple hydrophilic groups in the lignin structure (e.g., methoxyl, phenolic hydroxyl, aldehyde and carboxyl) can interact with cellulose via hydrogen bonding, hence connecting the carbon nanomaterials to the paper substrate.…”

“…Moreover, multiple hydrophilic groups in the lignin structure (e.g., methoxyl, phenolic hydroxyl, aldehyde and carboxyl) can interact with cellulose via hydrogen bonding, hence connecting the carbon nanomaterials to the paper substrate. Therefore, the role of lignin is twofold: (i) it promotes the aqueous dispersion of carbon nanomaterials [ 28 ], and (ii) serves as a cross-linking agent to bridge the cellulose microfibers with carbon nanomaterials ( Figure 6 ). This results in the formation of a compact layer protecting the substrate from the flame and preserving the paper integrity, which will also be responsible for the self-extinguishing properties.…”

“…Compared to other methods, the Meyer rod coating is a reproducible technique for the continuous large-scale preparation of uniform carbon nanomaterial films, which is critical for the formation of a protective barrier to limit soot transfer [ 25 ]. Furthermore, the combination of GnPs with CNTs in the correct proportions has the potential to yield synergistic effects [ 26 , 27 ], while the incorporation of lignin, the second most abundant natural polymer typically treated as a waste byproduct of the pulp and paper industry, can ensure high dispersion quality of nanomaterials [ 28 ], and provide good char-forming ability [ 29 , 30 , 31 ]. Considering the above, we successfully developed a cost-effective, high-performance and environmentally sustainable composite flame retardant with nanomaterial content as low as 4 wt %.…”